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Welding in confined spaces introduces synergistic hazards: oxygen displacement by shielding gases, accumulation of toxic welding fumes (manganese, hexavalent chromium), and fire/explosion potential. The MOST critical hazard is oxygen depletion and toxic fume accumulation because it can rapidly lead to unconsciousness or death. STSC principles emphasize anticipating and controlling confined space hazards with ventilation, atmospheric monitoring (oxygen, flammables, toxics), and confined space entry permits. Ventilation must maintain oxygen between 19.5–23.5% and contaminants below permissible exposure limits. Supervisors must ensure trained attendants, communication systems, rescue plans, and PPE (including supplied-air respirators when ventilation is insufficient). Noise and ergonomics are important but secondary to immediate life-threatening hazards. Electromagnetic fields are less significant compared to asphyxiation or poisoning. By prioritizing atmospheric safety, supervisors demonstrate hazard recognition, industrial hygiene control, and compliance with permit-required confined space standards central to the STSC framework.